I am a newbie programmer using Ruby, and this is my first question on Stack Overflow so please bear with me. Let's say I have two Hashes:
hash_one = { :key1 => :value1, :key2 => :value2, :key3 => :value3 }
hash_two = { :key4 => :value4, :key5 => :value5, :key6 => :value6 }
What would be the easiest way to move a key/value pair from hash_one (e.g. :key1 => :value1) into hash_two?
hash_two[:key1] = hash_one.delete(:key1)
delete removes key1 from hash_one and returns the value of key1. That value is taken as the parameter to set this key in hash_two.
Related
I have a user inputed string called x_value whose value contains something like ticker|high. Whenever there is a |, that indicates that the latter is a child of the former. The purpose of the method is to return a specific value within a hash.
sections = []
object.x_value.split('|').each do |part|
sections << part.to_sym
end
I then want to drill down the data hash and retrieve the value of the last key.
data = {"ticker":{"high":529.5,"low":465,"avg":497.25,"vol":7520812.018}}
In this example
data[sections[0]][sections[1]] returns the expected 529.5 value. However, the user may have different hashes and different levels deep of nested key/values. How can I write this?
I have tried data[sections], but that didn't work.
Use Enumerable#reduce
data = {"ticker" => {"high" => 529.5, "low" => 465,"avg" => 497.25,"vol" => 7520812.018}}
"ticker|high".split('|').reduce(data) { |dat,val| dat[val] } #=> 592.5
more example:
data = {"more_ticker" => {"ticker" => {"high" => 529.5, "low" => 465,"avg" => 497.25,"vol" => 7520812.018}}}
"more_ticker|ticker|avg".split('|').reduce(data) { |dat,val| dat[val] }
#=> 497.25
You could also use recursion:
def getit(hash, x_value)
recurse(hash, x_value.split('|'))
end
def recurse(hash, keys)
k = keys.shift
keys.empty? ? hash[k] : recurse(hash[k], keys)
end
data = {"ticker" => {"high" => 529.5, "low" => 465}}
getit(data, "ticker|high") #=> 529.5
getit(data, "ticker") #=> {"high"=>529.5, "low"=>465}
data = {"more_ticker" => {"ticker" => {"high" => 529.5, "low" => 465}}}
getit(data, "more_ticker|ticker|low") #=> 465
getit(data, "more_ticker|ticker|avg") #=> nil
I'm trying to get the first key and value key from a hash table in ruby. I don't know the key values of the hash because it is passed to the method. I cant find anywhere online how to find the first key/value as a separate hash table.
I think hash[0] will just try to find an element with a name 0 it just returns nil when I run the code.
I know I can find the key name and the value and then create a new hash from them but i wonder if there is an easier way to do this so I get a hash right away.
here is my code:
def rps_game_winner(game)
rock_in_hash = game.invert['R']
paper_in_hash = game.invert['P']
scissors_in_hash = game.invert['S']
if(rock_in_hash)
if(paper_in_hash)
return paper_in_hash;
elsif(scissors_in_hash)
return rock_in_hash
end
elsif(paper_in_hash)
if(rock_in_hash)
return paper_in_hash
elsif(scissors_in_hash)
return scissors_in_hash
end
end
key = game.keys[-1]
value = game.values[-1]
winner = {key => value}
return winner
end
game_one = { "Bob" => 'P', "Jim" => 'P' }
puts rps_game_winner(game_one)
This gets me the correct result the problem is I don't understand why it's -1 instead of zero...
And i was hoping there was a better way to get the first key/value pair of a hash table instead of creating new hash table with the key and value you retrieved from the previous table.
You can just do
key, value = hash.first
or if you prefer:
key = hash.keys[0]
value = hash.values[0]
Then maybe:
new_hash = {key => value}
There is a shorter answer that does not require you to use extra variables:
h = { "a" => 100, "b" => 200 , "c" => 300, "d" => 400, "e" => 500}
Hash[*h.first] #=> {"a" => 100}
Or if you want to retrieve a key/value at a any single position
Hash[*h.to_a.at(1)] #=> {"b" => 200}
Or retrieve a key/values from a range of positions:
Hash[h.to_a[1,3]] #=> {"b"=>200, "c"=>300, "d"=>400}
[hash.first].to_h
Another way to do it.
my_hash = { "a" => "first", "b" => "second" }
{ my_hash.keys.first => my_hash.values.first }
This works too
This question already has answers here:
Strange, unexpected behavior (disappearing/changing values) when using Hash default value, e.g. Hash.new([])
(4 answers)
Closed 5 years ago.
Lets say I have a Hash called person whose key is name and value is a hash having keys 'age' and 'hobby'. An entry in the hash person would look like
=> person["some_guy"] = {:hobby => "biking", :age => 30}
How would I go about specifying the default for the hash 'person'? I tried the following
=> person.default = {:hobby => "none", :age => 20}
but it doesn't work.
EDIT:
I was setting one attribute and expecting others to be auto-populated. For eg.
=> person["dude"][:age] += 5
and this is what I was seeing
=> person["dude"]
=> {:hobby => "none", :age => 25}
which is fine. However, typing person at the prompt, I get an empty hash.
=> person
=> {}
However, what I was expecting was
=> person
=> {"dude" => {:hobby => "none", :age => 25}}
Why It May Not Work for You
You can't call Hash#default if an object doesn't have the method. You need to make sure that person.is_a? Hash before it will work. Are you sure you don't have an array instead?
It's also worth noting that a hash default doesn't populate anything; it's just the value that's returned when a key is missing. If you create a key, then you still need to populate the value.
Why It Works for Me
# Pass a default to the constructor method.
person = Hash.new({hobby: "", age: 0})
person[:foo]
=> {:hobby=>"", :age=>0}
# Assign a hash literal, and then call the #default method on it.
person = {}
person.default = {hobby: "", age: 0}
person[:foo]
=> {:hobby=>"", :age=>0}
What You Probably Want
Since hash defaults only apply to missing keys, not missing values, you need to take a different approach if you want to populate a hash of hashes. One approach is to pass a block to the hash constructor. For example:
person = Hash.new {|hash,key| hash[key]={hobby: nil, age:0}}
=> {}
person[:foo]
=> {:hobby=>nil, :age=>0}
person[:bar]
=> {:hobby=>nil, :age=>0}
person
=> {:foo=>{:hobby=>nil, :age=>0}, :bar=>{:hobby=>nil, :age=>0}}
You can specify a hash's default value on instantiation by passing the default value to the .new method:
person = Hash.new({ :hobby => '', :age => 0 })
You can use Hash#default_proc to initialise a hash with default values dynamically.
h = Hash.new
h.default_proc = proc do |hash, key|
hash[key] = Hash.new(0) unless hash.include? key
end
h[0][0] # => 0
h[1][0] # => 0
h[0][0] = 1
h[0][0] # => 1
h[1][0] # => 0
I believe this has been asked/answered before in a slightly different context, and I've seen answers to some examples somewhat similar to this - but nothing seems to exactly fit.
I have an array of email addresses:
#emails = ["test#test.com", "test2#test2.com"]
I want to create a hash out of this array, but it must look like this:
input_data = {:id => "#{id}", :session => "#{session}",
:newPropValues => [{:key => "OWNER_EMAILS", :value => "test#test.com"} ,
{:key => "OWNER_EMAILS", :value => "test2#test2.com"}]
I think the Array of Hash inside of the hash is throwing me off. But I've played around with inject, update, merge, collect, map and have had no luck generating this type of dynamic hash that needs to be created based on how many entries in the #emails Array.
Does anyone have any suggestions on how to pull this off?
So basically your question is like this:
having this array:
emails = ["test#test.com", "test2#test2.com", ....]
You want an array of hashes like this:
output = [{:key => "OWNER_EMAILS", :value => "test#test.com"},{:key => "OWNER_EMAILS", :value => "test2#test2.com"}, ...]
One solution would be:
emails.inject([]){|result,email| result << {:key => "OWNER_EMAILS", :value => email} }
Update: of course we can do it this way:
emails.map {|email| {:key => "OWNER_EMAILS", :value => email} }
I'd like to save some hash objects to a collection (in the Java world think of it as a List). I search online to see if there is a similar data structure in Ruby and have found none. For the moment being I've been trying to save hash a[] into hash b[], but have been having issues trying to get data out of hash b[].
Are there any built-in collection data structures on Ruby? If not, is saving a hash in another hash common practice?
If it's accessing the hash in the hash that is the problem then try:
>> p = {:name => "Jonas", :pos => {:x=>100.23, :y=>40.04}}
=> {:pos=>{:y=>40.04, :x=>100.23}, :name=>"Jonas"}
>> p[:pos][:x]
=> 100.23
There shouldn't be any problem with that.
a = {:color => 'red', :thickness => 'not very'}
b = {:data => a, :reason => 'NA'}
Perhaps you could explain what problems you're encountering.
The question is not completely clear, but I think you want to have a list (array) of hashes, right?
In that case, you can just put them in one array, which is like a list in Java:
a = {:a => 1, :b => 2}
b = {:c => 3, :d => 4}
list = [a, b]
You can retrieve those hashes like list[0] and list[1]
Lists in Ruby are arrays. You can use Hash.to_a.
If you are trying to combine hash a with hash b, you can use Hash.merge
EDIT: If you are trying to insert hash a into hash b, you can do
b["Hash a"] = a;
All the answers here so far are about Hash in Hash, not Hash plus Hash, so for reasons of completeness, I'll chime in with this:
# Define two independent Hash objects
hash_a = { :a => 'apple', :b => 'bear', :c => 'camel' }
hash_b = { :c => 'car', :d => 'dolphin' }
# Combine two hashes with the Hash#merge method
hash_c = hash_a.merge(hash_b)
# The combined hash has all the keys from both sets
puts hash_c[:a] # => 'apple'
puts hash_c[:c] # => 'car', not 'camel' since B overwrites A
Note that when you merge B into A, any keys that A had that are in B are overwritten.